1. Field of the Invention
This invention relates to a radiation image detector capable of generating electric charges in accordance with a quantity of radiation or recording light irradiated to the radiation image detector when the radiation or the recording light, which carries radiation image information, is irradiated to the radiation image detector, the radiation image detector being provided with a charge accumulating section, at which the electric charges having been generated are accumulated as latent image charges, the radiation image detector being capable of detecting the radiation image information through irradiation of reading light to the radiation image detector. This invention also relates to a radiation image detecting system comprising the radiation image detector and reading light irradiating means for irradiating the reading light to the radiation image detector.
2. Description of the Related Art
Various radiation image detecting systems utilizing radiation image detectors have heretofore been proposed and used in practice in medical fields for recording of medical radiation images, and the like. The radiation image detectors utilized in the radiation image detecting systems are capable of generating electric charges in accordance with the quantity of radiation, such as X-rays, which carries radiation image information of an object and is irradiated to the radiation image detectors. The radiation image detectors are capable of accumulating the generated electric charges at charge accumulating sections and are thereby detecting the radiation image information of the object. With the radiation image detecting systems utilizing the radiation image detectors, the radiation image information is recorded by use of the radiation image detectors, and the radiation image information having been recorded in the radiation image detectors is read out as an electric signal.
As examples of the radiation image detectors described above, there have been proposed radiation image detectors, comprising: (i) a first electrode layer, which has transmissivity with respect to radiation for recording or with respect to recording light produced through excitation with the radiation for recording, (ii) a recording photo-conductor layer, which is capable of exhibiting electrical conductivity when it is exposed to the radiation or the recording light, (iii) a charge transporting layer, which acts approximately as an electrical insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrode layer, and which acts approximately as an electrical conductor with respect to electric charges having a polarity opposite to the polarity of the electric charges occurring in the first electrode layer, (iv) a reading photo-conductor layer, which is capable of exhibiting electrical conductivity when it is exposed to reading light, and (v) a second electrode layer having transmissivity with respect to the reading light, the layers being overlaid in this order. With the aforesaid examples of the radiation image detectors, latent image charges carrying radiation image information are accumulated at a charge accumulating section, which is formed at an interface between the recording photo-conductor layer and the charge transporting layer. (The aforesaid examples of the radiation image detectors are described in, for example, U.S. Pat. Nos. 6,268,614 and 6,770,901.)
Also, particularly, there has been proposed a radiation image detector, wherein second electrodes are constituted of a plurality of linear reading electrodes, and wherein the plurality of the linear reading electrodes and a plurality of linear auxiliary electrodes for outputting an electric signal having a level in accordance with the quantity of latent image charges having been accumulated at a charge accumulating section are arrayed alternately and in parallel. The proposed radiation image detector is described in, for example, U.S. Pat. No. 6,770,901. In cases where the second electrodes are constituted as the linear electrodes, the reading light is capable of passing through the regions between adjacent linear electrodes, and therefore the second electrodes need not necessarily have the transmissivity with respect to the reading light.
Heretofore, the radiation image detector described in, for example, U.S. Pat. Nos. 6,268,614 or 6,770,901 has been produced with a process, wherein the reading photo-conductor layer, the charge transporting layer, and the recording photo-conductor layer are overlaid on the plurality of the linear second electrodes, and wherein the first electrode layer is thereafter formed on the recording photo-conductor layer by use of a vacuum evaporation technique. Ordinarily, the reading photo-conductor layer, the charge transporting layer, and the recording photo-conductor layer are overlaid by use of a film forming process. However, the reading photo-conductor layer is a thin film having a thickness of as small as several tens of microns. In cases where the charge transporting layer, which has a markedly small thickness (i.e., a thickness of approximately 0.5 μm), is overlaid on the thin film constituting the reading photo-conductor layer, there is the risk that the smoothness of the charge transporting layer will not be capable of being kept good, and that the reliability of the radiation image detector will not be capable of being kept high. In particular, it may often occurs that the temperature, at which the charge transporting layer is formed, is higher than the temperature, at which the reading photo-conductor layer is formed. In such cases, the problems occur in that the smoothness of the charge transporting layer becomes bad, the charge transportability becomes low, and therefore the reliability of the radiation image detector becomes low.